The invention concerns a switchable support element for a finger lever of a valve train of an internal combustion engine, said support element comprising a housing, an inner element, a coupling means and at least one spring, the housing being telescoped with the e inner element which is biased away from m the housing by the spring and extends beyond an end of the housing by a head that comprises a support for the finger lever, the coupling means being configured for selectively coupling the housing to the inner element in an axially extended state of the housing and the inner element.
A generic support element of the pre-cited type is disclosed in DE 44 22 340 A1. This support element has the inherent drawback of a relatively large overall height. As a person skilled in the art will see from the figure, due to the compression spring being arranged under the inner element, a considerably large design space is required. If such a support element is to be integrated, for example, into existing engine designs, its relatively large height can lead to design space problems. Also, it is often not possible to deepen the reception bore for the support element in the cylinder head because one would penetrate into the region of inlet, outlet and cooling channels or the like.
Other known switchable support elements have a relatively large overall width due to their special concentric spring arrangement, or due to other design features.
It is an object of the invention to provide a support element of the pre-cited type in which the aforesaid drawbacks are eliminated.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that the spring is arranged substantially or entirely axially outside of the housing while being supported with one end in a region of the end of the housing and with a further end, on the head of the inner element in a vicinity of the support of the head.
This inventive concept also includes a solution in which a coil spring, known per se, surrounds the inner element concentrically outside of the housing. Preferably, however, it is intended to use torsion springs or clips which, according to a preferred embodiment of the invention extend at a radial distance from the support element. These torsion springs, also called leg springs, are positioned with their coils outside of the cylinder head so that other components such as walls, spark plugs, camshaft bearings etc., situated in this region are not affected.
Taken as a whole, the invention proposes a switchable support element that requires only a small design space and can thus be integrated in most cases into existing engine designs. Engine manufacturers therefore do not need to make complicated modifications to the overall design of the engines. Distances once defined, for instance the distance of the camshaft axis from the crankshaft axis and others, can be retained. In particular, due to the sideward shifting of the spring element, the proposed support element is relatively flat compared to prior art support elements, for example, compared to the support element disclosed in DE 197 10578 A1.
It is conceivable to use a variety of other spring elements such as leaf springs, flat coil springs, torque rods and the like.
The spring, which is also designated as a lost motion spring, possesses, despite its relatively compact dimensions, such a good spring rate that a reliable re-setting and retention of the inner element during contact of the finger lever with the run-off profile of the cam can be expected over the entire speed range of the internal combustion engine in which the lost motion function of the spring is required (speeds of, for example, up to about 2500 r.p.m.).
Other features of the invention concern advantageous configurations of the ends of the spring which is preferably made as a torsion spring. It goes without saying that in place of a single torsion spring as the spring means, a plurality of inter-inserted or adjoining springs may also be used.
According to one proposition of the invention, legs of the spring which emerge from front ends of the spring from the coils may have end extensions through which a fixing on the housing can be effected. In place of the extensions, the spring of the invention may also comprise loops or the like which can be mounted on pins on the end of the housing. As an alternative, it is proposed to have the legs surround the housing in the manner of a ring and support them in the direction toward the housing on an annular shoulder thereof.
The further end of the spring may be configured as a pair of arms that emerge centrally from the coils and extend toward the support element to again surround the support element in the region of the head of the inner element in the manner of a ring. A simply realizable fixing measure for these arms in the direction away from the housing is to support them on a separate securing element such as a circlip or on an annular shoulder of the inner element.
Alternatively, it is proposed that the legs of the one end of the spring emerge centrally from the coils and be supported on the end of the housing while the arms of the further end of the spring surround the inner element in the region of the head in the manner of a ring. A simple support surface for the arms in the direction toward the finger lever can be realized in this case in that they bear against a securing element like the aforesaid circlip or the like.
In order not to unnecessarily obstruct the sink-in movement of the inner element during the idling stroke of the inner element into the housing in the uncoupled state of the support element, it is proposed that the arms that surround the inner element in the manner of a ring comprise two inward bends that are in contact only with the inner element. Since, during this sink-in movement, the arm is bent towards the housing against the spring force of the spring, no important obstruction is created at the point of contact of the arm with the inner element.
Further, it must be remarked that the inventive configuration and arrangement of the spring offers a great amount of freedom in the designing and construction of the contacting finger lever that may be made, for example, as a thin-walled sheet metal finger lever. Thus, if required, the lower region of the finger lever that faces the support element may advantageously be configured with a larger thickness which would enhance its rigidity.
It is clear that the scope of protection of the invention extends to a great number of variations of the claimed configuration of the spring with its legs and arms. Further, in place of the torsion spring, it is also possible to use a clip or a clasp with its finger ends engaging the support element.
The invention will now be described with reference to the appended drawings.